[clang] [llvm] [PowerPC] Add intrinsics for rldimi/rlwimi/rlwnm (PR #82968)

[Chen Zheng via llvm-commits]

chenzheng1030 wrote:

> If you run into issues using normal integer ops, please file bugs. Most people aren't going to hand-tune their code like this; builtins like this are at best an ugly workaround.

Yes, a user should not try to write source code(using compiler builtins) to just emit one "powerful" instruction. Instead, it is compiler's responsibility to generate these instructions according to user's source codes.

I think the reason why these builtins were added is LLVM PowerPC target wants to keep its compatibility with XLC/C++ commercial compiler related to these builtins.

https://github.com/llvm/llvm-project/pull/82968